Method and Apparatus for Processing Ack Signal in a Wireless Local Area Network System

1. A signal processing method performed by an access point (AP) of a wireless LAN system supporting multiple resource units (RUs) for a data field, the method comprising: transmitting, by the AP, a downlink multi user physical layer protocol data unit (MU PPDU) for multiple receiving stations; after the MU PPDU is transmitted, determining, by the AP, multiple non-responding stations which have not transmitted immediate acknowledgement (ACK) frames corresponding to the MU PPDU to the AP; and transmitting, by the AP to the multiple non-responding stations, a single PPDU including a multi user block ACK request (MU-BAR) requesting ACK frames corresponding to the MU PPDU from the multiple non-responding stations.

2. The method of claim 1 , wherein multiple data fields for the multiple receiving stations are included in different resource units of the MU PPDU.

3. The method of claim 2 , wherein the MU PPDU includes a first signal field and a second signal field, wherein the first signal field includes a common control information for the multiple receiving stations, and wherein the second signal field includes identification information corresponding to the multiple receiving stations and allocation information corresponding to different resource units.

4. The method of claim 1 , wherein the MU-BAR includes identification information corresponding to the multiple non-responding stations and frequency resource information for a transmission of the ACK frames.

5. The method of claim 1 , wherein the MU PPDU includes a legacy field, a high efficient signal (HE-SIG) field, and a second data field, wherein the legacy field includes a legacy short training field (L-STF), a legacy long training field (L-LTF), a legacy signal (L-SIG) field, wherein the HE-SIG field indicates downlink resources for the multiple receiving stations, wherein a first subcarrier spacing is applied to the legacy field and the HE-SIG field and a second subcarrier spacing is applied to the second data field, wherein the first subcarrier spacing is four times greater than the second subcarrier spacing.

6. An access point (AP) of a wireless LAN system supporting multiple RUs for a data field, the access point comprising: a radio frequency (RF) unit transmitting and receiving radio signals; and a processor controlling the RF unit, and wherein the processor is configured: to control the RF unit so as to transmit a downlink multi user physical layer protocol data unit (MU PPDU) for multiple receiving stations; after the MU PPDU is transmitted, to determine multiple non-responding stations which have not transmitted immediate acknowledgement (ACK) frames corresponding to the MU PPDU to the AP; and to transmit, to the multiple non-responding stations, a single PPDU including a multi user block ACK request (MU-BAR) requesting ACK frames corresponding to the MU PPDU from the multiple non-responding stations.

7. The access point of claim 6 , wherein multiple data fields for the multiple receiving stations are included in different resource units of the MU PPDU.

8. The access point of claim 7 , wherein the MU PPDU includes a first signal field and a second signal field, wherein the first signal field includes a common control information for the multiple receiving stations, and wherein the second signal field includes identification information corresponding to the multiple receiving stations and allocation information corresponding to different resource units.

9. The access point of claim 6 , wherein the MU-BAR includes identification information corresponding to the multiple non-responding stations and frequency resource information for a transmission of the ACK frames.

10. The access point of claim 6 , wherein the MU PPDU includes a legacy field, a high efficient signal (HE-SIG) field, and a second data field, wherein the legacy field includes a legacy short training field (L-STF), a legacy long training field (L-LTF), a legacy signal (L-SIG) field, wherein the HE-SIG field indicates downlink resources for the multiple receiving stations, wherein a first subcarrier spacing is applied to the legacy field and the HE-SIG field and a second subcarrier spacing is applied to the second data field, wherein the first subcarrier spacing is four times greater than the second subcarrier spacing.